Traditional designs of internal combustion engines employ evaporative fuel control systems to control unwanted air pollution and loss of fuel due to evaporation of fuel from the tank, the carburetor, and other engine components. In particular, there is an evaporative fuel control system which employs a fuel vapor collection canister containing an adsorbent material, such as activated carbon, for adsorbing evaporative fuel, and a purge system for releasing the adsorbed fuel and supplying it to the engine during operation of the engine.
Conventional evaporative fuel control systems typically also include a leak check system employing different leak check methods to check for leakage of evaporative fuel (leak of vapor) to the atmosphere.
Conventional evaporative fuel control systems for an engine also exist wherein the systemchecks for evaporative fuel leaks after stop of the engine and refuel to a fuel tank. See JP No. 3412678.
Conventional evaporative fuel control systems for an engine also exist that provide a test mode which opens a purge passage between the fuel tank and an intake passage, and shuts an atmosphere open section, when the engine is in an idling state and a test signal is sent from a testing device to a control section. In this test mode, whether there is a failure in the evaporative fuel control system or not is determined based on a pressure variation of a purge passage toward the fuel tank over a predetermined time. See JP Laid-Open No. H10-89162.
One leak check method for an evaporative fuel control system for an engine utilizes an electric pressure reducing pump, a reference orifice, a pressure sensor, and a switching valve. In this leak check method, a reference pressure is primarily measured after the atmosphere is vacuumed by the pressure reducing pump through the reference orifice. A pressure is then measured after a certain time after the switching valve is switched such that the fuel tank is vacuumed. By comparing this pressure with the reference pressure, the occurrence of leakage (large leak greater than the reference orifice) is determined.
This leak check of the evaporative fuel control system is executed during normal operation of the vehicle (in fact during stop of the engine while stopping of the vehicle). It takes some time to conduct a leak check, since the pressure is measured while reducing the check passages of the system by the pressure reducing pump.
However, this increases the amount of time required to conduct a leak check in a checking process for completed cars in the factories, which may exceed an acceptable amount of process time required in assembly lines.